Composite ringsr circuits



March 23,1926.- 1,577,690

0. F. CASSADAY COMPOSITE RINGER CIRCUITS Filed May 21, 1919 4 Sheets-Sheet 1 March 23 1926.

1,577,690 0. F. gAssApAY COMPOSITE RINGER CIRCUITS Filed may 21, 1919 4 Sheets-Sheet 2 E R "21 I: "1,

ZZZ/52774711 l? W J 272171755] March 23 1926. 1,577,690

0. F. CASSADAY COMPOSITE RINGER CIRCUITS Filed May 21, 1919 4 bneets-Sheet 5 March 23 1926. 1,577,690 o. F CASSADAY COMPOSITE RINGER CIRCUITS 4 Sheets-Sheet 4 J ZZZ/51270111 I immfifisimiy ?atented Mar. 23, 1925.

ORMOND F. CASSADAY, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARD AND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

COMPOSITE RINGEB, CIRCUITS.

Application filed May 21, 1919. Serial No. 298,765.

T0 aZZ to [2.0m it may concern:

Be it known that I, Onaronn F. OASSADAY, a citizen of the United States of America, residing in Chicago, county of Cook, and state of Illinois, have invented certain new and useful Improvements in Composite Ringer Circuits, of which the following is a specification. V

lily invention relates to signaling systems in general and has to do most particularly with the socalled composite ringing circuits as are used in conjunction, with composite telephone and telegraph circuits.

Composite telephone and telegraph circuits as now in use have deficiencies in that, when signaling current is applied to signa a distant station it interrupts and interferes with the regular telegraph signals and the thumps or discharges from the telegraph circuits when in use will cause false signals to be transmitted.

An object of my invention is to produce a system of the above character which overcomes the above objections and which is simple in construction, most efficient in its operation and accomplishes signaling without the objections found in prior systems.

A feature of my invention is the provision of a relay of the vibrating type which is only responsive to signaling current of a high frequency and is non-responsive to the ordinary telegraphic discharges of the telegraph circuit.

7 Another feature of my invention is the provision of a circuit arrangement of telephonic devices in association with telegraphic devices and including my vibrating relay in association with other apparatus thereby providing an improved means for signaling a distant stationand eliminating the liabilities of false signaling due to telegraphic discharges, as well as interfering with the telegraphic devices when a distant station is signaled.

The novel features of the invention through the provision of which the above mentioned and other advantageousresults v are attained, will be explained by reference to the accompanying drawings, in which like reference characters in the several views denote like parts, and in which Fig. 1 is a front vie-wof the relay of my invention with the protective cap in section;

Fig. 2 is a left side elevation of Fig. 1';

'to the relay structure as illustrated in Figs.

1 to 4, inclusive, the relay of my invention comprises a U-shaped permanent magnet 2 to which is secured a soft yoke member 3 which is secured to the leg l of the permanent magnet 2 by means of a stud 5. The

stud-5 passes through suitable openings in the leg l of the magnet 2 and the yoke 3,

and the end which passes through the said openings is up set, as clearly illustrated in Fig. 3, to secure the yoke 3 to the magnet 2. A pair of electromagnet coils 6 and 7 are secured to legs 8 and 9 of the yoke member 3 by means of the screws 10, which screws 10 have screw-threaded engagement with suitable tapped openings in the cores 11 of the electromagnets 6 and 7. A mounting plate 12 of suitable insulation material such as bakclite or micarta is secured to the leg 13 of the permanent magnet 2, by means of a stud 1a, which stud 14 is provided with a threaded portion 15, that passes through suitable openings in the plate 12 andieg 1 A nut 16 is provided and has screw-threaded engagement with the threaded portion 15 of the stud 14, so that when the nut 16 is SLR'QWOLl down, it clamps the said mounting plate 12 to the pern'ianentmagnet 2. An L-shaped reed armature 17 is provided and is secured to the stud ii in any suitable manner, preferably by cutting a slot 18 in the stud 1 t of a size to receive the reed armature 17, and the armature. when thus placed may be soldered or anchored to the as a terminal for the said spring member 20. The free end of the spring is provided with a weight 23 secured to the free extremity of the spring in "any suitable manner, for purposes as will be more fully hereinafter described. The reed armature 17 is provided with an arm 24 with which the re silient spring member 20 normally in engagement. The arm 24 acts upon the siring 20 when the reed armature is vibrated. Terminals 25 and 26 are suitably secured to the mm'uiting plate 12 by means of rivets 27 and the tern'iinal ends 25 and 26' serve as terminals for the windings of the coils (i and 7, and the terminal ends 25 and 26 which are 'angularly disposed, extend through suitable openings in the mounting plate 12 and serve as terminals for external connections. Brackets 28 and 29 are provided and are secured to the mounting plate 12 by means of the rivets 30 and serve as a mounting means for the relay. A protective cap or cover 31 is pro vided and is slipped over the relay structure and held in place by means of a thumb nut '32, which nut has screw-threaded engagement with the threaded portion 33 of the stud 5.

When current passes through the coils 6 and 7, the reed armature 17 is acted upon, causing the said reed armature 17 and spring 20 to be vibrated. By reason of the 'L- shaped construction of the reed armature 17, it vib ates with a node at the point where the armature 17 impinges the cores of the electromagnets 6 and 7. and the vibrations of the angular portion 24 of the armature 17 at its end are the reverse of the vibrations between the node and the supporting stud 14. The rate of vibration of the spring 20 is much lower than that of the reed armature 17, partly because it is lighter than the reed armature, and partly because its weight is unequally distributed, due to the mass or weight 23 at its free end. The reed armature 17 and the spring 20 possess diverse motions and therefore, when the reed armature 17 and the spring 20 are vibrated, the armature 17 and spring 20 pull away from each other. The spring 20, due to its construction, can not follow promptly the vibrations of the reed armature 17, so that the contact between the said armature 17 tion, I will now describe in general the ap paratus as illustrated in Fig. 5, parts 1, 2 and 8, which shows a composite telephone and telegraph circuit embodying the features of my invention. Referring now to Fig. '5, part 1, at the left handside Ishow a local battery substation of a well-known type, and comprising the usual substation equipment. The local battery substation A terminates at the exchange in a line circuit L, including the usual combined drop signal and jack J. The cord circuit B comprises the usual answering plug AI and calling plug OP, a listening key LK which key vhen actuated connects the ope *ators set '0 to the cord conductors. A ringing key 1K also shown, which key, when actuated, connects the ringing generator G to the plug Cl for signaling purposes, and a clearing out signal or drop CL is provided for the usual supervisory purposes. A. CQll'lPO'SitQ ringing circuit C for signaling a distant station terminates at one end in a trunk jack TJ and associated therewith is a drop signal DS. A ringing relay RE is provided, which is normally energized and when (lo-energized connects ringing genera tor G for signaling purposes. 'A repeating coil RC is associated with an alternating current relay AC. A high frequency inter rupter I is provided and comprises an interrupter relay IR, a retard coil RD and an induction coil IC in association with a switching relay SW. Relay STV when actuat-ed associates generator G with the interrupter I, for purposes as will bemore fully hereinafter described. The high frequency relay HF is'also provided, which is preferably constructed as shown in Figs. 1 to 4, inclusive.

Referringn'ow to Fig. 5, part- 2, I here illustrate composite circuits D and D, which comprise the usual retardation coils HA. RA and 2 and HA respectively. Morse or telegraph sets TS and TS are operatively associated with the circuit D and locatedat a terminal point and sets TS and TS are operatively assoeiatedwith the eircuit D and located at a terminal point, as is well understood. The sets TS, TS, etc. comprise the usual Morse relay MR, key K and relay M for the usual sending and re ceiving purposes, as is well understood.

In Fig. 5, part 3, I illustrate composite ringer circuit E which is similar to the circuit illustrated in Fig. 5, part 1, and conr prises an interrupter I, which includes retardation coil RD, an induction coil IO,

an interruater relav IR and rin in en- .1 7 h C; C

eratorG. Ialso provide an alternating current relay AC, a'high frequency relay HF, re eating coil RC, a ringing relay 'RE' .anc its associated ringing generator 3. The circuit-E at its right end terminates 111 51 trunk ack TJ' and usual "drop signal DS The cord "circuit C for interconnecting purposes comprises the usual answering and calling plugs AP and CP, ringing and listening keys lR-K and LK for connecting respectively the ringing generator G and operators set to the cord conductors when actuated, and a clearing out drop signal CL for the usual purposes. I also show a called local battery substation F which terminates at the exchange in the usual drop signal D3 and jack J.

The lines L and L may be trunk or toll lines, and are shown as subscribers lines for illlustration purposes only.

Haring described in general the apparatus embodying the preferred form of my invention, I will now describe in detail the operation of the circuit as illustrated. Assuming now that the subscriber at the substation A initiates a call, the actuation of the hand generator thereat actuates the drop signal DS at the exchange and the operator noting the actuated drop signal DS inserts the answering plug AP of the cord circuit G into the jack J of the line, which insertion restores the drop signal DS. Theoperator now actuates her listening key LK to'connect her operators set 0 to the cord conductors and inquires the wants of the calling subscriber at substation A. Assuming further that it is the substation F at the distant exchange that is wanted, the operator inserts the calling plug GP into the trunk jack TJ and actuates the ringing key RK to connect the generator G with the trunk ack. The ringing current then flows from the ungrounded pole of the generator G, through the tip con tacts ofthe connected plug GP and trunk jack TJ, alternate contact 2 of the ringing relay RE, windings 3, 4, 5 and 6 of the repeating coil RC, conductor 7, condenser 8, through the winding of the alternating current relay AC, conductor 9, alternate contact 10 of relay RE, and the sleeve contacts of the connected plug CP and jack TJ to ground. The circuit of relay RE, which is normally energized, extends from battery through the winding of relay RE, and over conductor. 11, to ground at normal contact 12 of high frequency relay HF. The alternating current relay AC, upon actuation, closes its, alternate contact 13, closing an energizing circuit for the switching relay SiV, traced from battery, through the wind ing of relay SW and over conductor 14 to ground at alternate contact 13 of relay AC. Ringing current from generator G also passes through the high frequency relay HF, but as switching relay Sl/V is energized as soon as relay AC actuates, the circuit for relay HF is opened at normal contact 15 of relay Sl V and should the normal contact 12 of relay HF open, the ringing relay RE bein a slow-actim relay is held ener izedb b n. 7 2.)

due to its slow to release action, thus preventing a false signal being sent.

The switching relay SW upon energization closes its alternate contacts 16, 17 and 18 and the closin of alternate, contact 17 connects ringing generator G with the interrupter circuit l, the circuit being traced from the generator G over conductor 19, through alternate contact 17 of relay SN, conductor 20, normal contact 21 of relay B], through the winding of the interrupter relay IR, conductor 22, the winding 23 of the induction coil IC, conductor 24, to the other pole of the generator G This interrupted current is induced into the winding oil? the induction coil 1C and this high irerpicucy current extends from the winding 25 ot' the induction coil TC, through winding 26 oi the retardation coil RD, conductor 27, alternate contact 16 of switching relay SV, oycr conductor 28, through normal contact 29 of switching relay SWV, conductor 30, windings 31, 32, 33 and 34 of the repeating coil RC, conductor 35, condenser, 36, windings 37 and 38 of the high frequency relay HF, conductor 39, normal contact 40 of switch ing relay SW, conductor 41, normal contact 42 of relay SW, conductor 43, alternate contact 18 of relay S W, conductor 44., through the winding 45 of retardation coil RD to the other side of the winding 25 ot the induction coil 10. The high frequency current does not affect the drop signal D or the alternating current relay AC, but the high frequency relay HF is responsive to the current which passes through its windings 37 and 38 and causes the reed armature to vibrate to open the normally closed contact between the said reed armature and the resilient spring member, as previously de scribed, and the opening of normally closed contact 46 of relay HF, due to its Vibratioi'u opens the energizing circuit for ringing re lay RE (which relay RE is normally cn ergized when relay HF is at normal) permitting the same to de-cnergize. The relay RE upon de-energizatio-n closes its normal contacts 48 and 49 which connects current from the ringing generator G through normal'contact 48 of relay RE, normal coir tact 50 of trunk jack TJ, the winding oi dropsignal BS and normal contact 51 of trunk jack T5 to ground at normal contact 49 of relay RE. Current passing through the winding of the signal D8 actuates it.

The operator at the exchange, at which called substation F terminates, noting the actuated drop signal DS inserts an answering plug AP into the trunk jack TJ of the actuated drop and operates her listening key LK to connect her set 0 across the conductors of the cord C. She now inquires the wants of the calling subscriber and re-- ceiving the information that it is the subscriber at substation F that is wanted, inserts the calling plug CP into the jack J or uof the called line and actuatcs her ringing hey RK. The actuation of the ringing key RK connects ringing generator G to the call signal at the called. substation F, and the subscriber in response to the signal, removes his receiver from his switch hook. The sulscriber at the calling substation A and the subscriber at the called substation i are now in conversational circuit, which may be trac d over the heavily marked conduetors.

Assuming now that. the subscribers a the .:alling and called substations A and 1 have finished conversation, the subscriber at the substation A replaces his receiver and actuates his hand generator, causing current: to flow through the clearing out drop (L of the crud circuit C, thereby actuating the same. The operator seeing the actuated drop knows that the subscriber at substation A. has replaced his receiver and withdraws the answering and calling plugs AP and CP from the jacks J and TJ. The subscriber at the called substation F replaces his receiver and actuates his hand generator to operate drop CL of cord circuit ti. The

operator then withdraws the answering and calling plugs AP and GP :trom the jacks TJ and J. The apparatus used in establishing the connection described is now at normal and available for establishing other connections.

Assuming now that the subscriber at the substation F is a calling subscriber, the actuation of his hand generator at the substation causes the drop signal DS" to operate and the operator noting the signal, inserts the answering plug AP in the jack J" and actuatcs her listening key LK to connect her set across the calling line, and inquires the wants of the calling subscriber. It being the subscriber at substation A that is wanted, she inserts the calling plug CP into the jack TJ and actnat-es the ringing key 11K, thereby coimectmg generator current from generator to trunk iack TJ to actuate the alternating current relay AC, as is readily understood from the previous description. The relay AC upon energization closes its alternate contact 70, closing an energizing circuit for the switching relay SW, traced from battery, through the winding of relay SiV to ground at alternate contact 70. Relay SN upon energization closes its alternate contacts 29, 42 and 71. The closing of contact 71 connects generator G to the interrupter circuit I, causing high frequency current to be delivered from the interrupter circuit 1 through alternate contact 29, over conductor 28, normal contact 16 of relay S'W, windings 3, 4, and 6 of repeating coil RC, windings 72 and 73 of high frequency relay HF, normal contacts and 18 of relay SW conductor 43 to alternate contact 42 of relay SW. The

high frequency current generated by the devices I or 1 is of such a character that it does not a lfcct any ot the telegraphic instruments. The high frequency current actuatcs relay HF, which opens its normal contact 12 to allow relay RE to restore, and relay RE restoring, closes its normal contacts 2 and 10, connecting generator G to the drop signal DS to bring about its actuation. The operator at the distant exchange noting the signal, inserts hcr answering plug AP into the jack TJ and finding that itis substation A that wanted, inserts thecall- .ing plug GP into the jack J and signals in the usual manner, and in response to the si nal the subscriber at A answers and conersation may now he carried on. Disconnection is the same as previously described and a further description is not deemed necessary.

The telegraphic instruments may be used while telephonic connections are being carried on over the trunk circuit without in any way affecting the telephonic conversation or the telephone apparatus.

A mining thatv it desired to operate the telcgraphicset T 3 tosend a message to tele graphic station 'lb", the opening of contact 150 of the said hey K opens the circuit of relay .M. The relay M is normally held energized over a circuit traced from the positive pole ot the battery, through the winding of relay M, normal contact 150 of the key K, conductor 151, windings 52 and 53 of the retardation coil RA, conductor 28, windings 5st and of the retardation coil HA normal contact 56 of key K", and through the winding of relay M to the other pole of battery and to ground. The operation of key K for signaling purposes thus actuatcs the relays M and 3 causinq Morse relays MR and MB to energize anc (lo-energize for. signaling purposes, as is well understood. 11011 the key K of the telegraph set TS is actuated, the relay M at station TS is actuated. Likewise,'whcn lrys K and K are operated, relays M and M at stations T S and TS, respectively, are actuated. The thump or discharges from the telegraph circuits which may pass out over the line, do not a'tl'ect the high fro quency relays HF or HF, due to their con tion, so that no false operations of re lays lllil or R15) are brought about to cause the transmission of false impulses. The retardation coils RA, 11A, RA? and RA. are for the usual purposes, as is well understood in the art of composite circuit construction, whereby telegraph and telephone circuits may operate simultaneously over the same circuit.

lVhile I have illustrated'and described a preferred embodiment of my invention, I do not wish to be limited to the same as my invention is applicable with other circuit arrangements. Changes and modifications will also readily suggest themselves to those skilled in the art, and I, therefore, aim to cover all such changes and modifications as come within the spirit and scope of the appended claims. I

Having described my invention what I claim as new and desire to secure by United States Letters Patent is:

1. A system of the character described including a trunk circuit terminating in a pair of terminals, a high frequency generator for connection-t0 said trunk circuit, a high frequency relay and an alternating current relay in multiple circuit for each endof said trunk circuit, a normally energized relay for each end ofsaid trunk circuit, a central office signal associated with one of said terminals, and generator means for operating said central office signal, generator means for operatingthe said alternating current relay associated with the said one of said terminals, a pair of switch ing relays for said trunk circuit, means includin saidalternating current relay and one of said switching relays for connecting said high frequency generator to said trunk circuit to operate the high frequency relay at the other end of said trunk circuit to effect the normally energized relay of said other end of said trunk circuit to connect said first generator to said trunk circuit to operate the said central ofiice signal to notify the operator that a call is being extended over said trunk circuit.

2. A system of the character described in eluding a trunk circuit terminating in a pair of terminals, a high frequency generator connected in circuit with said trunk circuit, a high frequency relay and an alternating current relay in multiple circuit at each end of said trunk circuit, said relays being connected in circuit with said trunk circuit, a normally energized relay at each end of said trunk circuit, a central office call signal connected to one of said terminals, means controlled by said normally energized relay of said one terminal for operating said call signal, a low frequency generator associated with the other of said terminals, means for applying current from said last generator to said trunk circuit, a pair of switching relays for said trunlrcircuit, means including one of said alternating current relays and one of said switching relays controlled by said application of current for connecting said high frequency generator to said trunk circuit to operate thehigh frequency relay at the other end to eflect said energized .relay'of said one terminal to connect said first means in circuit With said call signal Whereby'saideall signal is caused to operate, telegraphic instruments connected to each conductor of said trunk-circuit, and means for so connecting said instruments that they are unaffected by the current from the said generators.

3. A system of the character described including a two conductor trunk circuit provided with a pair of terminals, switching relays for'each end of said trunk circuit, an individual alternating current relay, a high frequency relay and a normally energized relay for each end of said trunk circuit, the alternatingcurrent relay and the high frequency relay at each end of said trunk circuit being in multiple circuit with each other, high frequency generating means for connection to said trunk. circuit by one of said switching relays, a central office call signal connected to one of said terminals and'a generator adapted to be connected by one of said switching relays with said one terminal to-operate said call signal, ringing current means, means for connecting said ringing current means to the other end of said trunk, means including one of said alternating current relays and one of said switching relays responsive to said ringing current for connecting said high frequency generating means to said trunk circuit to operate one of said high frequency relays and one of said switching relays at said first terminal to effect said energized relay of said first terminal to connect said first generator to said one terminal to effect opera tion'of said ca'll signal to notify the central operator'that it is desired to extend a call over said trunk circuit.

4. A system of the character described in cluding a trunk circuit provided with a pair of. terminals, high frequency generating means for connection to said trunk circuit, a signal connected to one of said terminals, a generator for operating said signal, a normally energized relay for maintaining said generator out of circuit with said signal and said terminals, ringing current means, means for applying ringing current from said ringing current means to the other of said terminals, means including an alternating current relay and a switching relay responsive to said current for connecting said high frequency generating means to said trunk circuit, means controlled by said normally energized relay for connecting said first generator to said terminal and said signal, a high frequency relay connected with said terminal responsive to current from said high frequency generating means for de-energizing said normally energized relay to connect said first generator to said first terminal and said signal for operating thesan'ie, telegraphic instruments connect-ed to each conductor of said trunk circuit, and means for so connecting said instruments that they are unaffected by the current from said generators. i

5. A system of thecharacter described in.-

IUO

iiectc'dto each o'f the conductors' of said wi ait trunk circuit whereby telegraphic messages may be sent ea'chavay 'overe'aclrof said trunk conductors, aceritral oilice cail signal connected to eachof said te'i'n'iinals, generators for operating said signals,"ahigh frequency generating device, a high frequency relay and an'alternating current relay and a s'witchingrelay and a-norn ally energized relay operatively connected with each of said terminals, means for "applying ringing current to either of said terniinalst'o operate the alternating current relayan'd the switchingrelay at the sameterniinal to which said ringing current is applied to connect the as? sociated high frequency generating device withthe trunk'circuit tooperate the high frequency relay at the opposite end of said trunk circuit to street said'norinally energized relay at the opposite ear of said trunk circuit forconnecting the genera tor at that end with its associated signal to operate its associatedsignaithereby apprising the central ofiice operator of a call.

6. A system oi. the character described i11- eluding a two waytrunk ci'rcuit'provided with terminals, telegraphic instruments connected to each of the conductors of said trunk circuit whereby telegraphic messages may besent each way oyer e'ach'of said trunk conductors, a signal connected to each of said terminals,"an"individual generator for each of said signals ior' operating said" signa s, a normally energized relay for each terminal for normallymaintaining said generator out of circuit with itsassociated terminal and signal, a high frequency generating device and a high frequency relay connected with each ofsaid terminals, means controlled by said high frequency'relay for controlling said norn 'ia ily energized relay, switching means, means forappl *ingringing current to caterer saidterminiils for operating said switching means reconnect the associated high frequency generating device with the trunkcircuit to operatethe high frequency relay at the opposite end of said trunk circuitto operate thesaid first means to cause said normally energized relay to dc-energize thereby connecting the generator atthat end with its'associated terminal and signal to operatel'said' "sig'na'l, andtelephonic mcc'han'isn'i for'holding c'o'n versations over said't'runk circuit, said tele; phonic mechanism, signaling mechanismand telegra fliicmechanism being "so connected as not to interfere "with the operation eaclrother.

7*. A system of the character described including a two-way trunk" circuit provided with terminals, telegraphic instrument's conncctedto-each of theconductors of said trunk circu ts whereby telegraphic:messages wh s/o er "earl-160is id i y-1, "'5 ovum. i *f'ME-e w re trunk conductors, a signal connected to each of said terminals, an individual generator for 'e ach oi'lsaid signals foropeiating its associiited s gaarsgad generatornormally disconnected'ironi its associated signal and terminal y a normally energized relay, a high trequency generating device and a ngh frequency relayfconnected with each of said terminals, said normally energized reay being controlled one of said high frequency relays, switching means, means for applying ringing current to either of said terminals to actuate said switching means to connect the associated high frequency generating device 'wit h the trunk circuit to operate the high frequency relay at'the opposite end of said tii'inlccircuit "to 'cause'said normally energized relay to de-ciier izethereby connecting the generator at that endwith' its 'associated' terniinaland signalto operate said signal, aid high'frequeifcy rela' s beingso constructed and connected as to e unaffected by the telegraphic 'iinpi'llses when the telegraphic instruments are in'use.

S. A system of the character described including a two-way trunk circuit terminating at its opposite ends in jacks, a telephone line, a link' circuit connected to said telephone line and to saidtrunk circuit via one of said jacks, a central office signal connected with the otherjack ofsaid t'ru'nk'circuit, a switching relay'operatively associated with an alternating current relay connected to one" end ofsa'id trunk circuit to which saidlink circuit is connected, a generator for said trunk circuit for"actuating said signal, a higlifredhericy relay connected to the otliei-"en'd "or said trunk, a high treqaeney"generat r, a second switching relay, a generator operative-fly associated with the said link'circuit 'for applying generator current tosaid trunk circuit to operate said AJ'CI. relay whereby said first switching relay is actuated to connect said high fie q'uency generator to said trunk circuih'thereby causing thc actuation of: said'high fro-- quency relay, which relay causes the actuation of said second switchingrelay to c0iinect said 'firstgeuerator tosaid trunk circuit to eflect the actuation of said central 'oihcesignalto notify the operator at the distant end of thetrunk circuit that a coin Motion is desired, a called subscrihei"s line. and'a second link circuit connecting said trunk ciicuit'to said called line. i

"9. A system of the character described including a two-way trunk circuit te'rminat iu'gatits opposite ends in jacks,a telephone line, a 'linlficircuit connected wand- *t'e1e phonelineandto said trunk circuit viaone of"s "it1j'acks,'a central 'otlicds'ignalronn'ected witluthe' othenjack o snairuak circuit, a swiiching'relayw ,erfiVely" sociated withfaif alternating current to which said link circuit is connected, a second switching relay, a generator for said trunk circuit for operating said signal, a-

high frequency relay connected to the other end of said trunk, ahigh frequency generator, another generator adapted to be connected with the said link circuit for applying generatorcurrent to said trunk circuit to operate said A. C. relay whereby said first switching relay is actuated to connect said high frequency generator to said trunk circuit, thereby causing the actuation of said high frequency relay, which relay causes the actuation of said second switching relay to connect said first generator to said first trunk circuit to cause the actuation of said central oflice signal to notify the operator at the distant end of the trunk circuit that a connection is desired, a'called subscribers line, a second link circuit connecting said trunk circuit to said called line, and telegraphic instruments connected to each conductor on the said trunk circuit, said telegraphic and telephonic instrumentalities be ing so connected as not to interfere with the correct operation of each other.

10. A system of the character described including a calling subscribei"s line and a called subscribers line, a trunk circuit terminating at its ends in two different exchanges, a link circuit for connecting said calling subscribers line to one end of said trunk circuit at one exchange; a central ofties signal connected to the other end of said trunk circuit at the other exchange, means for said trunk circuit for actuating said signal, a high frequency relay, a high frequency generator, and a switching relay operatively associated with each end of said trunk circuit: the high frequency generator at one end adapted to operate the high frequency relay at the other end of said trunk ircuit via said trunk circuit, and the switching relay at said one end adapted to control the connection of said high frequency generator with said trunk circuit, a second switching relay for said trunk circuit, a ringing current generator, means for applying ringing current from said ringing cur-- rent generator to the end of the trunk circuit to which is connected said link circuit, said ringing current being of a frequency not to affect the high frequency relay opcratiyely associated with that end of the trunk circuit but causing the operation of oneof said switching relays, thereby connecting the high frequency generator with the trunk circuit and causing the operation of the high frequency relay at the opposite end of the trunk circuit, the opera tion of the high frequency relay at the distant end of the cord circuit causing the operation of said second switching relay to connect said first means in circuit with said signal to effect actuation of said signal at said other exchange thereby notifying, the operator that a connection is desired, and a second link circuit at said other exchange for connecting said trunk circuit to said called subscribers line.

11. A system of the character described including a calling subscribers line and a called subscribers line, a trunk circuit terminating at its ends in two different e:- changes, a link circuit for connecting said calling subscribers line to said trunk circuit at one of said exchanges; a central office signal connected to said trunk circuit at the other of said exchanges, a generator for operating said signal, an alternating current relay, a high frequency relay, a high frequency generator and a switching relay operatively associated with each end of said trunk circuit; the high frequency generator at one end of said trunk circuit adapted to operate the high frequency relay at the other end of said trunk circuit via said trunk circuit, and the switching relay at said one end adapted to connect the high frequency generator to the trunk circuit, ringing current means, a second switching relay for said trunk circuit, means for applying ringing current to the end of the trunk circuit to which is connected said link circuit, said ringing current being of a frequency not to affect the high frequency relay associated with that end of the trunk circuit but causing the operation of the alternating current relay of that end to effect the operation of one of said switch-- ing relays, thereby connecting the high frequency generator with the trunk circuit and causin the operation of the high frequency relay at the opposite end of the trunk circuit, the operation of the high frequency relay atthe distant end of the cord circuit causing the operation of said second switching relay to connect said first generator with said trunk circuit to actuate the central office signal at the distant end of the cord circuit, notifying the operator that a connection is desired, a second link circuit for connectin said trunk circuit to said called subscribers line, and telegraphic instruments connected to each conductor of said trunk circuit, said telegraphic and tele phonic instrunientali'ties being so connected and operable as not tointerfere with the correct operation of each other.

Signed by me at Chicago, in the county of Cook and State of Illinois, this 19th day of May, 1919.

ORMOND F. CASSADAY. 

